The conversion operation could be started on Jan 6th, so on Jan 9th you will have the Hive and the answer of how much Hive 1 HBD is equivalent to. :)

No, you do not.

The question is, how much a HBD is worth in Hive at the time of the snapshot. As you correctly pointed out in a different corner of this thread, pre-snapshot and post-snapshot prize is likely to be fundamentally different so no 3.5 day median is going to reflect that fairly (BTW, the conversion starting 1.75 days before the snapshot is surely more fair than the one starting at snapshot).